Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2010
Publication Date: 3/1/2011
Citation: Saha, B.C., Cotta, M.A. 2011. Continuous ethanol production from wheat straw hydrolysate by recombinant ethanologenic Escherichia coli strain FBR5. Applied Microbiology and Biotechnology. 90(2):477-487.
Interpretive Summary: Any lignocellulosic biomass, upon pretreatment and enzymatic hydrolysis, generally produces a mixture of sugars. The utilization of all the sugars is essential for the economical production of ethanol. The conventional ethanol fermenting yeast or bacterium cannot ferment multiple sugars to ethanol. Our research unit has developed a recombinant bacterium that can ferment mixed multiple sugars to ethanol. Previously, we evaluated the batch production of ethanol by this recombinant bacterium from agricultural residues such as wheat straw, rice hulls, and barley straw. In order to produce ethanol industrially, the fermentative microorganism needs to be robust. We have now evaluated the long term performance of this recombinant bacterium in continuous culture using wheat straw hydrolyzate and found that the bacterium was quite stable. This information is very important for the use of the recombinant bacterium for continuous production of ethanol from any lignocellulosic biomass. Continuous production of ethanol offers an avenue for reduction of its production cost.
Technical Abstract: Continuous production of ethanol from alkaline peroxide pretreated and enzymatically saccharified wheat straw hydrolyzate by ethanologenic recombinant Escherichia coli strain FBR5 was investigated under various conditions at controlled pH 6.5 and 35 deg C. The strain FBR5 was chosen because of its ability to ferment both hexose and pentose sugars under semi-anaerobic conditions without using antibiotics. The average ethanol yield from the available sugars (21.9-47.8 g/l) ranged from 8.8 to 17.3 g/l (0.28 to 0.45 g/g available sugars, 0.31-0.48 g/g sugar consumed) with ethanol productivity of 0.27-0.78 g/l**-1 h**-1 in a set of 14 continuous culture (CC) runs (16-105 days). During these CC runs, no loss of ethanol productivity was observed. This is the first report on the continuous production of ethanol by the recombinant bacterium from a lignocellulosic hydrolyzate.